On midengined cars and driving - Page 2 - LotusTalk - The Lotus Cars Community
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post #21 of 166 (permalink) Old 11-27-2003, 05:50 AM
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fastspider

Not to argue, but the S1 Elise was known for its "twitchy" rear end. To say that the car doesn't want to spin is not accurate - it does want to spin if you get near it's limits - maybe you weren't at or near the limit? Or maybe you are a better driver than most? Knowing what a car is doing is the key and the Elise/Exige are one of the best for telling you what is happening - it's up to the driver to hear what it is saying and reacting correctly.

The Exige helped some of these traits with wider wheels/tires and the benefit of real downforce. The S2 Elise is supposed to be much more "tame" at the limit than the S1. Many suspension revisions were made to achieve this.

To tell someone with no mid-engine experience that the Elise doesn't want to spin is asking for trouble. All it takes is one lift in a corner to do it or tapping the brakes mid-corner.
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post #22 of 166 (permalink) Old 11-27-2003, 09:29 AM
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Meat is exactly right. Also mid-engine means that SNAP oversteer is exactly that. I think it was stated earlier in this thread, the Fed Elise (like the S2) has induced understeer from the factory to make it safer for most drivers. With this setup the car should be safer on public roads.
As another example of factory induced understeer, the Boxster comes with 205's on the front and 255s on the rear. This together with the suspension setup and a rear brake pressure regulator ensures that the back will never step out under braking situations. Adding traction control stops the back stepping out under acceleration.
At the track, I have traction control OFF and run 245's all round. This balances the car nicely.
I hope this helps understanding.

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post #23 of 166 (permalink) Old 12-01-2003, 11:36 AM
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Interesting posts to this question...

I won't say midengine cars are easier or more difficult to drive, but the physics of distribution of weight makes mid-engine cars more responsive. To use Randy's analogy of the hammer, it takes a lot more force to spin a hammer around the mid point of the handle and an equal amount of force to stop it spinning.

Worse is a 2 headed hammer like a 944 with engine in front and tranny in the rear, the equal to a dumbbell.

In comparison the major elements of mass in a mid-engine car are near the center of gravity (CG). This differentiates weight distribution versus weight placement. It takes much much less force to get it to spin and equally little force to get it to stop spinning.

So, in real life the driver experiences a rapid transition from stable to a spin in a mid-engine car (but typically at much high lateral g-force) and equally faster recovery and equal ease in over correcting. The big benefit is rapid response and changes in direction (little force needed to rotate).

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post #24 of 166 (permalink) Old 12-01-2003, 12:10 PM Thread Starter
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Except that a large portion of the force required to rotate a midengined car is already present from the inertia of the car. For example, if the engine is in the front, and the car is moving forward, the engine will want to continue to move forward. So rotating is actually being fought by this inertia. One of the major components in understeer.

On the other hand, in a car with the engine in the back, the engine also wants to move forward under inertia. And as long as the car is perfectly straight to the direction of travel, that inertia just propels the car. But when you start to turn, that engine will still want to keep moving forward, which is now at a rotation point from the direction of travel.

So there is a major difference in the physics. The front engined car will want the front to continue straight. Not spinning. Just plowing. A rear engined car will want the engine to continue straight, which means the back end is coming around.

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post #25 of 166 (permalink) Old 12-01-2003, 01:24 PM
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Randy,

I think we are basically in agreement here.

I was just trying to point out that mid-engine cars are likely to be more responsive due to the placement of the major component of weight (engine+tranny) at or near the CG. I wasn't trying to argue that mid-engine cars are more stable.

At the same time I totally agree with your explanation that a front engined car is inherently more stable. However a front or rear engine car is not as responsive. I think where we are getting confused is that the physics of stability is not the same as the physics of responsiveness.

Cool?
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post #26 of 166 (permalink) Old 12-01-2003, 02:35 PM Thread Starter
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Yep! I agree that the midengined also means it is more responsive and is a positive if you know what you are doing.

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post #27 of 166 (permalink) Old 12-01-2003, 03:04 PM
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If I may add a question. How does non-power steering affect the mid engine balance...asides using more force on the wheel?

I've driven several Boxsters/S' and always felt the sense of balance (and confident) with the car while cornering. Driving the Euro Elise, I didn't really feel as confident.

I'm unsure how to describe it but it felt as if I was starting to approach the traction limits, even thought there was no way I could be that close, because I wasn't really pushing the Elise.

I'm not sure if the feel is due to the lack or power steering, shorter wheel base, or stiffer suspension? Perhaps what I was feeling was the slight and momentary traction loss from rough pavements while cornering?

That being said, I think the Elise will be more challenging to drive that other car (except maybe the rear engine 911). You know, I may be wrong, but I THINK there was a bit of rear engine feel to it also.
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post #28 of 166 (permalink) Old 12-01-2003, 03:19 PM
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My MR2 is non power steering, no differance in balance vs a p.s. version. Not really sure what you were feeling, maybe your not use to something that light. My understanding is that car is pretty beat up, not sure how well the alignment, tire pressure etc. is on it. With a 60% rear bias, you'll be aware of it.
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post #29 of 166 (permalink) Old 12-01-2003, 03:52 PM
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Quote:
Originally posted by LarryB
Not really sure what you were feeling, maybe your not use to something that light. My understanding is that car is pretty beat up, not sure how well the alignment, tire pressure etc. is on it. With a 60% rear bias, you'll be aware of it.
True. It's a very light car but w/o the power steering, it didn't feel light. Or maybe I'm just weak.

Seriously, I did feel a bit of a front end shudder at freeway speeds. I mentioned it to the salesperson, who then said the car has been driven hard. I have a feeling maybe the tire balance (or maybe pressure) may be off.
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post #30 of 166 (permalink) Old 12-01-2003, 04:05 PM Thread Starter
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A very light midengined car will be extra sensitive to any imbalance in the front tire/rim/brakes.

I agree that PS will not make much difference except for how it feels in the tight bits.

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post #31 of 166 (permalink) Old 12-01-2003, 04:15 PM
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Someone else has mention this & I notice it as well. The steering response at lower speeds is sluggish- in the sense that it has a "slow" manual steering ratio. Then again it's that way in the MR2, which at 1000lbs heavier then the Euro Elise & with skinner OEM front tire took a bit of muscle at parking lot speeds (BTW one of the benefits of going to lower profile tires, short stiff sidewall, really don't feel a need for p.s.)
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post #32 of 166 (permalink) Old 12-01-2003, 04:55 PM
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IMHO, my Exige has the best steering feel I have ever experienced. It tells you exactly what it is doing - right now. There is no delay, no wondering. The rear starts to come out under trail-braking and you just steer into it ever so slightly and nail the throttle and life is good again!

Around the paddock the steering is a bit heavy, but you get used to it. At speed, you really don't even notice that you don't have power steering.

When my friend first got his 190S (before I had my Exige) and I would drive it, I would also feel like the rear was coming around before it really was. I think this "feeling" might be inherent to new drivers of mid-engined cars. The physics are different and you really need be more smooth than even with a car like the S2000.
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post #33 of 166 (permalink) Old 12-01-2003, 05:27 PM
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IMHO...

heavy cars need PSteering... or little or no caster = little or nil straight line stability. Virtually all front drive cars need PSteering to mask torque steer.

PSteering masks "feel". GM sedans & Japanese cars in NAmer are typically over boosted and generally feel "light", ie easy to steer, but have virtually no feel. As a driver it's like driving a video game, you as the driver ends up driving to optimize the PSteering vs optimizing the traction.

The ultimate case of driving to maximize the driver aids was my experience driving a BMW X5 on track and finding that traction control, anti-skid & stuff intruded so heavily on the what the driver did that it was nearly impossible to do anything "stupid". The systems would always override the driver's "stupid" inputs. Thus to maximize performance and to get lap times down I had to drive to minimize the intrusion of the "driver aids", in order to allow them to maximize traction. Instead of driving the four tire patches I was driving a video game!

Light car without PSteering = GRINS!!!

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post #34 of 166 (permalink) Old 12-02-2003, 07:27 AM
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Allan, you may be confusing confidence with numbness. I have not driven any boxsters to compare with the Elises' steering "feel" but from the way I read your post you didn't like the fact you felt the roadway through the car. You could of covered the same stretch of road in another vehicle and not noticed the rough surface or stress cracks around the corner but that does'nt mean they do not exist. I think that is why people love to drive this car, it tells you exactly what it is doing and reacts to exactly what you tell it to do. I took that same car for a spin recently and don't remember feeling anything weird with the chassis but do plan on taking it for a more comprehensive test sometime this week.
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post #35 of 166 (permalink) Old 12-02-2003, 08:38 AM
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I'm hoping they'd let me take another test drive again.

I think my issue with the power steering may have been when I was taking a slow turn (possible when turning right or left from stop lights/signs), hence the weight was more noticeable. It's been a while since I drove a car without power steering (Fiat Bartone in '89).

Perhaps my concerns about the traction, while cornering may have been when I hit a bump during a turn?

It's not that I didn't like the Elise. It's just the handling dynamics are different. In regards, to the Boxster, factoring out the power (or lack of), it handles well enough that any average joe can handle the car well until they hit the limits. In contrast, I can see the Elise requiring more attention and skill. (I can relate to Randy’s posts about caution when driving a mid-engine car now). The result is that the Elise is a car that's more challenging and engaging to drive.

Hmm. I think I need another test drive. I hope test drivers aren't limited to one per customer.
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post #36 of 166 (permalink) Old 12-04-2003, 11:10 PM
 
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Nice discussion...


Good clear explanations from Randy and others.
Did i understand correctly that he gives driver training?
If so, i'm sure i'll book some if he ever comes to this side of the ocean...

I recently had a drift and powerslide training, awesome fun!
The Elise is so well designed it really wants to go where you point it's nose slightly understeered.
I find it quite hard to spin on purpose.
But the margin between controlled drift and uncontrolled spin is very small, and u have to be quite an experienced driver to get it right (i only managed a few times, spun a lot .. but hey, it was first outing like that...)

I utterly love its responsiveness and it IS twitchy ESpecially in the wet... roundabouts will teach you that
And yes... you'll discover bumps and little thingies in roads that you believed were perfectly smooth before.

But... no hard braking or clutching in corners, and be carefull on cold tyres. It's so easy to make a mistake.
They tried their best to get all the pro's from mid-engine/rearwheel powered, and design countermeasures for con's of 'hammer-effect'... and succeeded quite well.
U have to have a sensitive butt to feel the 8/10th, and i'm sure in time i'll get close to 10/10th... but i'll make sure not to try and find my limit on public roads, too many obstacles.

Top 5 things i think of the Elise:
* it is a drivers car, not for posers ('droeftoeters' in Dutch)
* when it's not raining, the roof is off (you wait till it poors/snows)
* slow in, quick out for corners
* slippery when wet
* best modifications: driver training and noisy exhaust (tunnels!)

Seloc is down, so i ended up here.
Thought i might as well contribute...

And... while i'm at it, compliment you on a nice forum!
Good luck with the waiting, it's well worth it though!


chrs, Julie
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post #37 of 166 (permalink) Old 12-05-2003, 02:53 AM
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HI JUlie,
Welcome to the board. Lots of you folks from SELOC have been very helpful on this board!
Chris
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post #38 of 166 (permalink) Old 12-05-2003, 03:04 AM
 
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Thanks Chris!


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post #39 of 166 (permalink) Old 12-17-2003, 07:22 PM
 
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Quote:
Originally posted by Julie
Good clear explanations from Randy and others.
Did i understand correctly that he gives driver training?
If so, i'm sure i'll book some if he ever comes to this side of the ocean...
Count me in too!
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post #40 of 166 (permalink) Old 01-06-2004, 06:17 PM
 
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Just thought I'd throw out a few comments, as there seems to be some confusion on two issues:

Polar Moment of Inertia, and
Fore/Aft weight distribution

I think it's a bit confusing to label front engined cars as intrinsically understeering and rear engined cars the opposite. Rather, nose heavy cars tend to understeer, rear heavy the opposite. Naturally, the engine placement tends to determine the relative balance of the car. However, as in the case of the E36 M3, the car is essentially 50/50 weight balanced, and is not an understeering car with equal sized tires front and rear, although it is front engined.

On this issue of weight distribution, the heaviest axle tends to operate at the highest slip angles when cornering. This difference in slip angles front to rear determines understeering/oversteering attitude. In rear heavy cars like a Pcar, this is compensated for by increase rear tire/wheel width and decreasing rear roll stiffness through tuning suspension tuning. In this regard, notice that the Elise, which is rear heavy like a rear engined Pcar, runs no rear sway and has a 50 to 30mm delta in front/rear tire widths.

As to PMI, two cars can have the same exact weight, and same exact weight distribution at the wheels shown by corner scales, yet have vastly different PMIs. The closer the distribution of mass to the CG, the lower the PMI. Low PMI cars, like my last car (Honda S2000) as well as the Elise are quicker to get away from the driver, but also quicker to get back in line. In short, as stated above, low PMI cars have quicker reflexes, and drivers need better/quicker skills to deal with them at the limit.

Dunno if that helps or not, but thought I'd jump in and play.
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